Rounding up fascinating news and research in the field of forensic science.

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Month: November 2015

What is your expertise within forensic science and what does this type of job role typically involve?

Forensic entomology can be divided into three groups: stored-product, urban and medico-legal (or medico-criminal) entomology. I specialize in the field of medicolegal forensic entomology. Generally speaking, forensic entomologists can estimate a postmortem interval (PMI) or time since death based upon the presence (or lack thereof) of insects collected on or near a body. Certain families of insects arrive in a predictable manner on corpses, especially the calliphorid flies (blow flies). Based upon the ages of specimens collected, a PMI can be estimated. Age of the specimens is directly related to the temperatures that the insects are experiencing; the higher the temperature (obviously to a certain limit), the faster they grow.

In a best-case scenario, when a body is found, a forensic entomologist should be called and he or she would collect and process the insect evidence. The second best scenario would be that properly trained law enforcement personnel would collect the insect evidence and then send it to a forensic entomologist for processing.

On occasion, forensic entomologists have to testify in court, just as would any other expert witness. The testimony usually focuses on time of death, but not always. Sometimes a body may have been moved and the calliphorids present can sometimes help determine such a thing. There was a case where a woman was murdered in a parking lot in the city of Jacksonville (Duval County). Her body was dumped in rural Clay County, but not before those city flies had a chance to deposit eggs on her body. The trial was held in Duval County.

Calliphorid female flies are attracted to areas of trauma on a body, where they will deposit eggs. Sometimes the trauma is not noticeable to the naked eye, but can be determined during autopsy. But forensic entomologists know that flies congregate and deposit eggs on areas of trauma on a body.

In September 2006, I received a call from the Jacksonville Sheriff’s Office that the body of an elderly man had been found in a culvert off of I-10, a major highway. I did not know what a culvert was until this case (for those who do not know, it is a tunnel that carries water under a road). It was necessary to climb down a steep angled wall to make an entomological collection. When I reached the body, I noticed that the man had hundreds of calliphorid larvae around his neck despite a lack of visible wounds or bruised skin. I told the detectives that the medical examiner would find the cause of death to be strangulation. I got a lot of strange looks from the detectives that day, but the autopsy showed the man had indeed been strangled to death.

I guess you could say that being a forensic entomologist requires getting very dirty, too. The first time I ever returned from a death scene, my husband had to have the car detailed because it smelled like human decomposition. But as horrific as it sounds, I continue to be fascinated by what calliphorid larvae can reveal about death and decomposition and how they can help solve crimes.

What led you to become involved in forensic entomology?

I thought I wanted to be a veterinarian, and one of the ways to get into vet school is to major in entomology. On the first day of my first entomology class, the professor handed out an article about the Body Farm in Tennessee. I changed my mind about wanting to be a veterinarian that instant.

What in particular was the focus of your PhD research in forensic entomology?

The main focus of my doctoral research was to study the life cycle of the forensically important calliphorid, Chrysomya megacephala (the oriental latrine fly). The main focus of my research was to study their development rates at different ambient temperatures.

Historically, calliphorid development rates have been studied by placing a few hundred calliphorid eggs in a cup (or cups) in a rearing chamber set to a certain temperature. The time is monitored as the larvae grow through three larval stages, a puparial stage, and then emerge as adults.

But the problem with testing in this manner is that calliphorid masses generate heat. Even a small amount of maggots can generate heat above ambient, thus the set chamber temperature is not really the temperature that the growing larvae/pupae are experiencing. For the development research, I used 10 larvae per container; an amount not capable of generating heat above ambient temperature.

Liver is a standard feeding substrate for calliphorid larvae in colony. But the small amount of liver needed for only 10 larvae per Petri dish dried up quickly, killing the larvae, so I developed a liver agar feeding substrate that would not dry up1. Then I was able to study precisely how the larvae developed at eight different temperatures.

This was grueling work in which larvae were checked at 4-hour intervals 24/7 for most of the duration of the development research, which took 15 months. As I had no funding to hire anyone to help me, I trained my husband to do it. He took the day shift, going back and forth to the lab every 4 hours as I tried to get some sleep. I spent nights (from 9 PM to 9 AM) in the lab. I was so sleep-deprived that it would have been dangerous for me to drive back and forth during the middle of the night.

There were times when we had to examine every larva individually to determine stage. This required looking at the anal spiracles of a larva under a microscope with a gentle but steady hand. During all those months of research when we were sleep-deprived and miserable, we never squished or killed a larva. I am very proud of that.

I also studied different size maggot masses and their respective temperatures as they grew in age, size and volume. And finally, I studied different models that could potentially be used to calculate age of a larva (or larvae). Most forensic entomologists use a linear model to estimate a PMI, but insect development is not linear, especially that of calliphorids.

Do you believe there are any common misconceptions surrounding this field of work?

There are too many to list, but I will name a few.

It is nothing even remotely similar to anything seen on TV.

Sadly, I know of only one person who is a full-time forensic entomologist in the USA (in Texas). Most who received their M.S. and PhDs studying forensic entomology are not teaching or practicing forensic entomology. They may take a case or testify in court on occasion, but that is rare.

Despite the potential importance of collecting insect evidence at death scenes, it is not done. The vast majority of detectives, crime scene technicians, etc., have no idea how to collect insect evidence and forensic entomologists rarely get called to process the insect evidence at death scenes.

Do you think that there are any significant gaps in research in forensic entomology?

Yes. I would say the biggest problem in this field is the poor quality of research, especially when it comes to studies regarding development rates of forensically important insects. Most (almost 80%) of the manuscripts published in peer-reviewed journals in the past 30 years lack replication and have poor experimental design. This is an embarrassment to the science and needs to change. But, there are many dedicated scientists in this field who are trying to do good work.

Finally, how do you feel about the extent to which forensic entomology is harnessed in legal investigations?

Forensic entomology is overlooked much of the time. Collection of insect evidence is not difficult, but as I mentioned above, such evidence is rarely–if ever–collected.